Julia version of Matplotlib griddata?

[Kaj Wiik]

Is there a Julia version of irregularly spaced data gridding that does

zi = griddata(x,y,z,xi,yi), i.e. all arguments are 1d vectors? It seems that Julia interp and contour packages require x, y, z[x,y].

https://scipy.github.io/old-wiki/pages/Cookbook/Matplotlib/Gridding_irregularly_spaced_data.html

Thanks,

Kaj

[Steven G. Johnson]

(You can always call the Matplotlib function from Julia via PyCall.)

[Kaj Wiik]

Yes, I tried that but for some reason, couldn't get natgrid recognized by matplotlib... One way would try to call natgrid library (libncarg) directly...

Thanks,

Kaj

[Josef Heinen]

You can use the GR framework, e.g.

srand(0)

xd = -2 + 4 * rand(100)

yd = -2 + 4 * rand(100)

zd = [Float64(xd[i] * exp(-xd[i]^2 - yd[i]^2)) for i = 1:100]

using GR

contour(xd, yd, zd, colormap=44)

If you only need the gridded data, use the GR gridit function, e.g. (to obtain a 200 x 200 grid):

x, y, z = GR.gridit(xd, yd, zd, 200, 200)

[Kaj Wiik]

Thanks Josef.

I tried GR contour but got identical datapoint errors. It seems that it's not trivial to use unique() other than vectors...could not get it working. In fact it seems that the reported datapoints are not in fact identical:

julia> contour(c[1,:],c[2,:],c[3,:])

 ***   IDENTICAL DATA POINTS.

   NDP =12629   IP1 =    1   IP2 =  346   XD=1.02114e-99   YD=0.478687

 ERROR DETECTED IN ROUTINE   IDTANG.

julia> c[:,1]

3-element Array{Float64,1}:

     1.02114e-99

     0.478687   

 56193.8        

julia> c[:,346]

3-element Array{Float64,1}:

     1.38697e-84

     0.477974   

 56196.2        

I tried also to call natgrid directly but it seems to be a can of worms.

Kaj

[Kaj Wiik]

I dug this problem bit deeper, it seems that my unique is working but GR.contour seems to be complaining even of close coordinates. I tried converting everything to Float32 but that didn't help either:

julia> contour(cf[3,:],cf[2,:],cf[1,:])

 ***   IDENTICAL DATA POINTS.

   NDP =12629   IP1 =   23   IP2 = 3286   XD=56192.9   YD=0.55634

 ERROR DETECTED IN ROUTINE   IDTANG.

julia> cf[:,[23,3286]]

3x2 Array{Float32,2}:

     0.0          6.64646e-20

     0.55634      0.555965   

 56192.9      56192.9        

Strange...

[Kaj Wiik]

Forgot to mention that in the first GR.contour attempt I had x and z swapped...